Methane, burning

As for the conventional methane burning cycles the IGCC plants can be modified... 

FIGURE H.3 When methane burns, it forms carbon dioxide and water. The blue color is due to the presence of C2 molecules in the flame. If the oxygen supply is inadequate, these carbon molecules can stick togelher and form soot, thereby producing a smoky flame. Note that one carbon dioxide molecule and two water molecules are produced for each methane molecule that is consumed. The two hydrogen atoms in each water molecule do not necessarily come from the same methane molecule the illustration depicts the overall outcome, not the specific outcome of the reaction of one molecule. The excess oxygen remains unreacted. 

C06-0006. How much heat is required to raise the temperature of 25.0 g of water from 25 °C to 65 °C on a methane-burning stove (see Table b-II ... 

FIGURE H.4 When methane burns, it forms carbon dioxide and water. The blue color is due to the presence of C2 molecules in the flame. If the oxygen supply is inadequate, these carbon molecules can stick together and form soot, thereby producing a smoky flame. 

Let s look more closely at spontaneous processes and at the thermodynamic driving forces that cause them to occur. We saw in Chapter 8 that most spontaneous chemical reactions are accompanied by the conversion of potential energy to heat. For example, when methane burns in air, the potential energy stored in the chemical bonds of CH4 and 02 is partly converted to heat, which flows from the system (reactants plus products) to the surroundings ... 

Demonstrate combustion of some alkanes. Use a Bunsen burner to show complete and incomplete combustion of methane. Burn a range of alkanes to show the variation in ease of ignition - pentane and hexane are highly flammable but liquid paraffin and paraffin wax need pre-heating and/or a wick. 

FURNACE Basis is 1 mole of methane burned with 30% excess air. 

Two important questions are asked about every chemical reaction (a) How much product is produced and (b) How fast is it produced The first question involves chemical equilibrium and the second question belongs to the domain of chemical kinetics. (We dealt with kinetics in Experiment 20). Some reactions are irreversible and they go to completion (100% yield). When you ignite methane gas in your gas burner in the presence of air (oxygen), methane burns completely and forms carbon dioxide and water. 

Since the maximum attainable temperature is sought, we assume complete adiabatic (Q = 0) combustion. With the additional assumptions that the kinetic- and potential-energy changes are negligible and that there is no shaft work, the overall energy balance for the process reduces to AH = 0. For purposes of calculation of the final temperature, any convenient path between the initial and final states may be used. The path chosen is indicated in the diagram. With one mole of methane burned as the basis for all calculations,... 

On the basis of 1 mol of methane burned with 25 percent excess air, the air entering the furnace contains ... 

A 10-15% mixture of methane in air may cause an explosion. Explosions in mines are known as "firedamp explosions". Also, huge garbage dumps in cities can cause dangerous explosions due to the production of methane. Methane burns with a light blue flame and is decomposed when it is heated strongly. 

When methane burns in air, the combustion is represented by the equation —... 

The methane burns to form water, and the carbtjn is deposited as very finely divided carbon, which finds extensive use as a filler for rubber for automobile tires,... 

Do you notice a correlation Iron rusting and methane burning are exothermic and spontaneous. The reverse reactions are endothermic and nonspontaneous. Based upon reactions such as these, some nineteenth-century scientists concluded that all exothermic processes are spontaneous and all endothermic processes are nonspontaneous. However, you need not look far for evidence that this conclusion is incorrect. For example, you know that ice melts at room temperature. That s a spontaneous, endothermic process. 

The dynamic reachon in which a fuel, such as hydrogen gas or methane, burns may seem quite different from the relatively calm redox reactions that take place in batteries. However, the burning of fuel shown in Figure 21-11 also is an oxidation-reduchon reachon. What happens when hydrogen burns in air ... 

Methane is burned in a furnace with 100% excess dry air to generate steam in a boiler. Both the air and the methane enter the combustion chamber at 500°F and 1 atm, and the products leave the furnace at 2000°F and 1 atm. If the effluent gases contain only CO2, H2O, O2, and N2, calculate the amount of heat absorbed by the water to make steam per pound of methane burned. 

Methane burns in a furnace with 10% excess air, but not completely, so some CO exits the furnace, but no CH4 exits. The reactions are ... 

Methane, CH4(g), is the main constituent of namral gas. In excess oxygen, methane burns to C02(g) and H20(f), whereas in limited oxygen, the products are CO(g) and H20( ). Which would result in a higher temperature a gas-air flame or a gas-oxygen flame How can you tell ... 

From these experiments of Bone, from those of Henry mentioned in Chapter VI, and from those of Landolt,5 it has been concluded that hydrogen has been found to bum before methane at low temperatures in contact with platinum catalysts, and even at relatively high temperatures in platinum tubes 5 and that methane burns before hydrogen when exploded or when kept in borosilicate bulbs at moderate temperatures. 

Therefore, because Hp,oducts can be either more or less than Heactants the sign of AH indicates whether heat is absorbed or released in the change. We determine the sign of AH by imagining the heat as a reactant or product. When methane burns in air, for example, we know that heat is produced, so we show it as a product (on the right) ... 

Figure 6.6 Enthalpy diagrams for exothermic and endothermic processes. A, Methane burns with a decrease in enthalpy because heat leaves the system. Therefore, Hf,nsi < Hinitiai, and the process is exothermic AH < 0. B, Ice melts with an increase in enthalpy because heat enters the system. Therefore, Hfinai > Hinisai. and the process is endothermic AH > 0.

In the mid-19 century, some thought that the sign of the enthalpy change (AH), the heat added or removed at constant pressure (qp), was the criterion for spontaneity. They thought that exothermic processes (AH < 0) were spontaneous and endothermic ones (AH > 0) were nonspontaneous. This hypothesis had a lot of support from observation after all, many spontaneous processes are exothermic. All combustion reactions, such as methane burning, are spontaneous and exothermic ... 

Which of these processes are nonspontaneous (a) methane burning in air (b) a teaspoonful of sugar dissolving in a cup of hot coffee (c) a soft-boiled egg becoming raw ... 

The equation which represents the volume relations and the amount of heat evolved when methane burns in oxygen, is as follows —... 

Reactions Between Nonmetals Although we can identify reactions between metals and nonmetals as redox reactions, it is more difficult to decide whether a given reaction between nonmetals is a redox reaction. In fact, many of fhe mosf significanf redox reactions involve only nonmetals. For example, combustion reactions such as methane burning in oxygen are oxidation-reduction reactions. 

On the contrary, an excess of oxygen leads to deep oxidation producing mainly carbon dioxide and water. Mechanism of methane burning includes the following stages [28b] ... 

We work out the energy value of methane as follows. The molar mass of methane is 16.0gmol k When 16.0 g of methane burns, 890 kJ of heat is produced. When 1 g of methane is burned, 890/16.0 = 56 kJ of heat is produced, so that the energy value of methane is 56kjg k The energy values of common fuels are shown in Table 13.3. 

REALITY CHECK The mass of methane burned is less than 1 mol, so less than 890 kJ will be released as heat. The answer has two significant figures as required by the given quantities. 

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